This project is concerned with the control of gene expression and two aspects of this problem are currently being investigated. Control of gene expression may be exerted at the levels of initiation of transcription. We have studied the mechanisms of transcriptional control in two bacterial operons, the lac operon and the biotin operon. Currently we are studying the control of the programmed pattern of transcriptional initiation during the infectious cycle of bacteriophage T4. We are also concerned with the control of expression and the function of the actin gene in S. cerevisiae. Most RNA molecules are post-transcriptionally altered in a series of reactions collectively known as RNA processing. It is now clear that RNA processing plays a major role in the expression of eukaryotic genes. The recent elucidation of eukaryotic gene structures has revealed a new principle of organization. Eukaryotic genes are frequently interrupted by non-coding sequences known as intervening sequences or introns. These sequences are removed from RNA precursors in a new processing reaction called RNA splicing. We were the first to demonstrate the RNA splicing reaction in vitro - in this case with yeast tRNA precursors. We are continuing the study of the tRNA splicing reaction and propose procedures for the investigation of mRNA splicing. Powerful new techniques have recently been developed allowing the in vitro alteration of genes and their return to the organism (transformation). The most powerful of the mutagenic strategies requires the organic synthesis of oligonucleotides by techniques which derive from the pioneering efforts of Khorana. We propose to use these techniques to synthesize oligonucleotides to produce precise alterations of genes in order to study the mechanism of control of RNA synthesis.